Experiments on blood vessels: (1) Electron microscopic study of the effect of spasm on small and medium sized arteries. (2) Electron microscopic study of the arteries and arterioles in hypertensive animals. (3) Electron microscopic study of arterial endothelium after infusion of vasoactive amines. (4) Light and electron microscopic study of the arterial wall after microinjection of foreign materials. Experiments on the myocardium: (1) Light and electron microscopic study of the effect of massive pulmonary embolism or of pulmonary stenosis on : the myocardium of the right ventricle (rat and dog). (2) Light and electron microscopic study of the "wavy fibers" in myocardial infarcts produced in the dog, at varying stages of the ischemic injury.